Of course, the reiteration of the seismic hazard to Californians will be nothing surprising, but what is new is the warning that the southern portion of the fault “looks like it’s locked, loaded and ready to go.”
Why is this eminent seismologist making these alarming statements? Well, the fact is that there has not been a major release of stresses in the southern portion of the San Andreas fault system since 1857. In simple terms, the San Andreas is one of many fault systems roughly marking the border between the Pacific and North American tectonic plates. Both plates are moving in an approximately northerly direction, but the Pacific plate is moving faster than its North American counterpart, meaning that stresses between the plates are constantly building up.